Expression, Purification and Molecular Structure Modeling of Thioredoxin (Trx) and Thioredoxin Reductase (TrxR) from Acidithiobacillus ferrooxidans

Isolation, Sphalerite Bioleaching, and Whole Genome Sequencing of Acidithiobacillus ferriphilus QBS3 from Zinc-Rich Sulfide Mine Drainage

The genus Acidithiobacillus has been widely used in bioleaching, and novel strains in this genus, such as A. ferriphilus, have also been confirmed to possess bioleaching capabilities. In this study, an Acidithiobacillus ferriphilus strain, QBS3, was isolated from zinc-rich sulfide mine drainage using the gradient dilution method. QBS3 is a Gram-negative, 1.3 µm rod-shaped bacterium with small red colonies. It showed a high iron oxidation efficiency of 0.361 g/(L·h) and a sulfur oxidation efficiency of 0.206 g/(L·d). QBS3 has sphalerite bioleaching ability; using QBS3 for pure sphalerite bioleaching, 18.8% of zinc was extracted in 14 days at 1% pulp density. Whole genome sequencing was performed on QBS3. Functional prediction showed that 9.13% of the genes were involved in replication, recombination, and repair. Bioleaching-related genes were analyzed, including iron and sulfur oxidation genes, and carbon and nitrogen fixation genes. For iron oxidation, the Cyc2→RusA pathway and Iro→RusB pathway were found in QBS3. In terms of sulfur oxidation, QBS3 has an incomplete SOX system and lacks the SDO gene, but Rho and Trx may complement the SOX system, enabling QBS3 to oxidize sulfur. QBS3 has multiple sets of carbon fixation genes, and nitrogen fixation genes were also identified. A hypothetical sphalerite bioleaching model is proposed; this study provides a theoretical basis for the zinc sulfide ore bioleaching industry.

Purification of thioredoxin reductase from Spirulina platensis by affinity chromatography and investigation of kinetic properties

The thioredoxin system consists of thioredoxin (Trx), thioredoxin reductase (TrxR) and nicotinamide adenine dinucleotide phosphate (NADPH). Spirulina platensis, which is one of the blue-green algae in the form of spiral rings, belongs to the cyanobacteria class. Spirulina platensis can produce Trx under stress conditions. If it can produce Trx, it also has TrxR activity. Therefore, in this study, the TrxR enzyme was purified for the first time from Spirulina platensis, an algae the most grown and also used as a nutritional supplement in the world. A two-step purification process was used: preparation of the homogenate and 2',5'-ADP sepharose 4B affinity chromatography. The enzyme was purified with a purification fold of 1059.51, a recovery yield of 9.7 %, and a specific activity of 5.77 U/mg protein. The purified TrxR was tested for purity by SDS-PAGE. The molecular weight of its subunit was found to be about 45 kDa. Optimum pH, temperature and ionic strength of the enzyme were pH 7.0, 40 °C and 750 mM in phosphate buffer respectively. The Michaelis constant (Km) and maximum velocity of enzyme (Vmax) values for NADPH and 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB) are 5 μM and 2.2 mM, and 0.0033 U/mL and 0.0044 U/mL, respectively. Storage stability of the purified enzyme was determined at several temperatures. The inhibition effects of Ag+, Cu2+, Al3+ and Se4+ metal ions on the purified TrxR activity were investigated in vitro. While Se4+ ion increased the enzyme activity, other tested metal ions showed different type of inhibitory effects on the Lineweaver-Burk graphs.

Heat and phosphate starvation effects on the proteome, morphology and chemical composition of the biomining bacteria Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a Gram negative, acidophilic, chemolithoautotrophic bacterium that plays an important role in metal bioleaching. During bioleaching, the cells are subjected to changes in the growth temperature and nutrients starvation. The aim of this study was to gather information about the response of the A.ferrooxidans Brazilian strain LR to K2HPO4 starvation and heat stress through investigation of cellular morphology, chemical composition and differential proteome. The scanning electron microscopic results showed that under the tested stress conditions, A. ferrooxidans cells became elongated while the Fourier transform infrared spectroscopy (FT-IR) analysis showed alterations in the wavenumbers between 850 and 1,275 cm(-1), which are related to carbohydrates, phospholipids and phosphoproteins. These findings indicate that the bacterial cell surface is affected by the tested stress conditions. A proteomic analysis, using 2-DE and tandem mass spectrometry, enabled the identification of 44 differentially expressed protein spots, being 30 due to heat stress (40°C) and 14 due to K2HPO4 starvation. The identified proteins belonged to 11 different functional categories, including protein fate, energy metabolism and cellular processes. The upregulated proteins were mainly from protein fate and energy metabolism categories. The obtained results provide evidences that A. ferrooxidans LR responds to heat stress and K2HPO4 starvation by inducing alterations in cellular morphology and chemical composition of the cell surface. Also, the identification of several proteins involved in protein fate suggests that the bacteria cellular homesostasis was affected. In addition, the identification of proteins from different functional categories indicates that the A. ferrooxidans response to higher than optimal temperatures and phosphate starvation involves global changes in its physiology.